Projection device and projection-type video display device

ABSTRACT

An illumination device includes an optical element including a hologram recording medium capable of diffusing a coherent light beam, the hologram recording medium comprising a plurality of regions, each region diffusing a coherent light beam to an illuminated region corresponding to that region, and an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium. The coherent light beam incident to a position existing in each region of the hologram recording medium is diffused to an entire region of the illuminated region corresponding to the region in order to illuminate the entire region of the illuminated region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/821,091, filed Mar. 6, 2013, the entirety of which is incorporatedherein by reference, which in turn is the National Stage ofInternational Application No. PCT/JP2011/070515, filed Sep. 8, 2011,which designated the United States.

FIELD OF THE INVENTION

The present invention relates to a projection device and aprojection-type video display device displaying a plurality of videos byusing a coherent light beam, and more particularly, to a projectiondevice and a projection-type video display device capable of allowingoccurrence of speckles to be inconspicuous.

BACKGROUND OF THE INVENTION

A projection-type video display device, including a screen and aprojection device which projects a video image on the screen, has beenwidely used. In a typical projection-type video display device, atwo-dimensional image as a basic image is generated by using a spatiallight modulator such as a liquid crystal micro display or a DMD (digitalmicromirror device), and the two-dimensional image is magnified andprojected on a screen by using a projection optical system, so that avideo is displayed on the screen.

As the projection device, various types including a commercializedproduct called an “optical type projector” have been proposed. In ageneral optical type projector, the spatial light modulator such as aliquid crystal display is illuminated by using an illumination deviceincluding a white light source such as a high pressure mercury lamp, andan obtained modulation image is magnified and projected on the screen byusing lenses. For example, Patent Literature 1 listed below discloses atechnique where a white light beam generated by a supper-high pressuremercury lamp is divided into three primary color components R, G, and Bby a dichiroic mirror, the light beams are guided to spatial lightmodulators corresponding to the primary colors, generated modulationimages corresponding to the primary colors are combined by a crossdichiroic prism to be projected on the screen.

As an application of the projection device and the projection-type videodisplay device, a projection device which projects video imagecorresponding to each screen on a plurality of the screens is known. Inaddition, a technique where signals representing different images can beoutput from one information processing terminal is also known, and videois displayed on a plurality of the screens by using the technique andthe projection device.

A plurality of the projection devices are needed in order to project thevideo image corresponding to each screen on a plurality of the screens.At this time, although a plurality of the spatial light modulators and aplurality of the projection optical systems are needed, it has beenconsidered that the projection device can be miniaturized by commonlyusing the illumination device illuminating the spatial light modulators.

However, the illumination device of the related art uses a high pressuremercury lamp, an LED, or the like as a light source to spread a lightbeam of the light source and transmit the light beam. In theillumination device of the related art, since the light beam is spread,there is a loss in light intensity, and there is a problem in that anoptical system becomes large.

Further, high intensity discharge lamp such as a high pressure mercurylamp has a relatively short lifecycle, and in the case where the lamp isused for an optical type projector or the like, the lamp needs to befrequently replaced. In addition, since a relatively large opticalsystem such as a dichiroic mirror is needed in order to extract thelight beams of the primary color components, there is a problem in thatthe size of the whole apparatus is increased as described above.

In order to cope with this problem, a type using a coherent light sourcesuch as a laser is also proposed. For example, a semiconductor laserwhich is widely used in industries has a very long lifecycle incomparison with the high intensity discharge lamp such as a highpressure mercury lamp. In addition, since the laser source is a lightsource capable of generating light having a single wavelength, aspectroscopic apparatus such as a dichiroic mirror is unnecessary, sothat there is an advantage in that the whole apparatus can beminiaturized. Further, since the diameter of the light beam of the lasercan be easily controlled, a loss of light may not easily occur.

On the other hand, in the type using the coherent light source such as alaser source, there is another problem in that speckles occur. Thespeckle is a punctate pattern which occurs when the coherent light beamsuch as a laser beam is irradiated on a scattering plane. If the speckleoccurs on the screen, it is observed as punctate luminance irregularity(brightness irregularity), so that it becomes a factor of exertingphysiologically bad influence on the observer. The reason why thespeckles occur in the case of using the coherent light beam is that thecoherent light beams reflected from portions of the scatteringreflecting plane such as a screen have very high coherency, and thespeckles are generated through interference therebetween. For example,in Non Patent Literature 1 listed below, theoretical review of theoccurrence of speckles is made in detail.

In the type of using the coherent light source, since there is anintrinsic problem in that the speckles occur, techniques for suppressingthe occurrence of speckles have been proposed. For example, PatentLiterature 2 listed below discloses a technique where a scattering plateis irradiated with a laser beam, an obtained scattered light beam isguided to a spatial light modulator, and the scattering plate is drivento rotate by a motor, so that speckles are reduced.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2004-264512 A-   Patent Literature 2: JP 6-208089 A

Non Patent Literature

-   Non Patent Literature 1: Speckle Phenomena in Optics, Joseph W.    Goodman, Roberts & Co., 2006

SUMMARY OF THE INVENTION

As described above, with respect to the projection device and theprojection-type video display device using the coherent light source,the techniques for reducing speckles which have been proposed up to nowmay not effectively and sufficiently suppress the speckles. For example,in the method disclosed in Patent Literature 2 described above, sincethe laser beams irradiated on the scattering plate are scattered, aportion of the laser beams are lost without contribution to videodisplay. In addition, the scattering plate needs to be rotated in orderto reduce the speckles, the mechanical rotation mechanism becomes arelatively large apparatus, and the power consumption is increased.Moreover, although the scattering plate is rotated, the position of theoptical axis of the illumination light beam is not changed, so that thespeckles occurring due to the diffusion on the screen may not besufficiently suppressed.

The inventors have researched based on the problems describedhereinbefore, so that the inventors contrived a projection device and aprojection-type video display device displaying a plurality of videos byusing a coherent light beam, which are capable of allowing speckles tobe inconspicuous and miniaturizing optical systems. In other words, thepresent invention is to provide a projection device and projection-typevideo display device which can display a plurality of videos and whichare capable of allowing speckles to be inconspicuous and miniaturizingoptical systems.

According to the present invention, there is provided a first projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

-   -   an optical element including a hologram recording medium where        information is multiplexedly recorded in each position so as to        allow a coherent light beam to be diffused to a plurality of        regions;    -   an irradiation device configured to irradiate the optical        element with the coherent light beam so as to allow the coherent        light beam to scan the hologram recording medium;    -   spatial light modulators configured to be illuminated with the        coherent light beam which is incident from the irradiation        device to the hologram recording medium to be diffused to the        plurality of regions; and    -   projection optical systems, each projection optical system        projecting modulation image obtained on each spatial light        modulator on corresponding screen,    -   wherein the coherent light beam, which is incident to each        position of the hologram recording medium to be diffused, is        illuminated on a plurality of the spatial light modulators.

According to the present invention, there is provided a secondprojection device displaying video corresponding to each screen on aplurality of the screens, including:

-   -   an optical element including a hologram recording medium capable        of reproducing an image of a scattering plate corresponding to        each illuminated region in a plurality of the illuminated        regions, and the images of the scattering plates being        multiplexedly recorded at each position of the hologram        recording medium;    -   an irradiation device configured to irradiate the optical        element with the coherent light beam so as to allow the coherent        light beam to scan the hologram recording medium;    -   spatial light modulators, each spatial light modulator disposed        to position which overlap each illuminated region; and    -   projection optical systems, each projection optical system        projecting modulation image obtained on each spatial light        modulator on corresponding screen,    -   wherein the coherent light beam, which is incident from the        irradiation device to each position of the hologram recording        medium, reproduces the image of each scattering plate in each        illuminated region.

According to the present invention, there is provided a third projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

-   -   an optical element including a hologram recording medium capable        of diffusing a coherent light beam, the hologram recording        medium including a plurality of regions;    -   an irradiation device configured to irradiate the optical        element with the coherent light beam so as to allow the coherent        light beam to scan the hologram recording medium;    -   spatial light modulators, each spatial light modulator being        illuminated with the coherent light beam which is incident from        the irradiation device to each region of the hologram recording        medium to be diffused; and    -   projection optical systems, each projection optical system        projecting modulation image obtained on each spatial light        modulator on corresponding screen,    -   wherein the coherent light beam, which is incident to each        position existing in each region of the hologram recording        medium to be diffused, is overlappedly illuminated on the        corresponding spatial light modulator.

According to the present invention, there is provided a fourthprojection device displaying video corresponding to each screen on aplurality of the screens, including:

-   -   an optical element including a hologram recording medium capable        of reproducing an image of a scattering plate corresponding to        each illuminated region in a plurality of the illuminated        regions, and the hologram recording medium including a plurality        of regions corresponding to the images of the scattering plates;    -   an irradiation device configured to irradiate the optical        element with the coherent light beam so as to allow the coherent        light beam to scan the hologram recording medium;    -   spatial light modulators, each spatial light modulator disposed        to position which overlap each illuminated region; and    -   projection optical systems, each projection optical system        projecting modulation image obtained on each spatial light        modulator on corresponding screen,    -   wherein the coherent light beam, which is incident from the        irradiation device to each position existing in each region of        the hologram recording medium, reproduces the image of the        scattering plate corresponding to each region in the        corresponding illuminated region.

In any one of the first to fourth projection device of the presentinvention, the irradiation device may include:

-   -   a light source configured to generate the coherent light beam;        and    -   a scan device configured to change a propagation direction of        the coherent light beam from the light source and allow the        coherent light beam to scan the hologram recording medium.

In any one of the first to fourth projection device of the presentinvention, the coherent light beam from the light source may beirradiated to one point of the scan device, the coherent light beamreflected from the one point of the scan device may constitute adiverging flux from the one point, and the diverging flux may beincident on the hologram recording medium.

In any one of the first to fourth projection device of the presentinvention,

-   -   the coherent light beam from the light source may be irradiated        to one point of the scan device, and the coherent light beam        reflected from the one point of the scan device may constitute a        diverging flux from the one point, and    -   the projection device may further include a parallel light        generation unit which propagates each light beam constituting        the diverging flux in a certain direction to generate parallel        light flux and allows the parallel light flux to be incident on        the hologram recording medium.

In the third or fourth projection device of the present invention, theirradiation device may include:

-   -   a light source configured to generate the coherent light beam;        and    -   a scan device configured to change a propagation direction of        the coherent light beam from the light source and allow the        coherent light beam to scan the hologram recording medium,    -   the light source may include a plurality of light source units        which emit a plurality of coherent light beams,    -   a plurality of the coherent light beams emitted from a plurality        of the light source units may be illuminated to the same point        on the scan device, and    -   each coherent light beam reflected from the same point on the        scan device may constitute diverging flux from the same point,        and each diverging flux may be incident on the corresponding        region of the hologram recording medium.

In the third or fourth projection device of the present invention, theirradiation device may include:

-   -   a light source configured to generate the coherent light beam;        and    -   a scan device configured to change a propagation direction of        the coherent light beam from the light source and allow the        coherent light beam to scan the hologram recording medium,    -   the light source may include a plurality of light source units        which emit a plurality of coherent light beams in substantially        parallel directions,    -   each coherent light beam emitted from a plurality of the light        source units may be irradiated at corresponding point on the        scan device, and    -   each coherent light beam reflected at each point on the scan        device may constitute diverging flux from the corresponding each        point, and each diverging flux may be incident on the        corresponding region of the hologram recording medium.

According to the present invention, there is provided a fifth projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

-   -   an optical element including a plurality of light diffusion        elements, each light diffusion element capable of changing a        propagation direction of an incident light beam;    -   an irradiation device configured to irradiate the optical        element with the coherent light beam so as to allow the coherent        light beam to scan each light diffusion element;    -   spatial light modulators, each spatial light modulator being        illuminated with the coherent light beam which is incident from        the irradiation device to each light diffusion element so that a        propagation direction thereof is changed, and    -   projection optical systems, each projection optical system        projecting modulation image obtained on each spatial light        modulator on corresponding screen, and    -   wherein the propagation direction of the coherent light beam        incident to each position of the optical element is changed by        the corresponding light diffusion element so that the coherent        light beam is overlappedly illuminated on the corresponding        spatial light modulator.

According to the present invention, there is provided a sixth projectiondevice displaying video corresponding to each screen on a plurality ofthe screens, including:

-   -   an optical element including a plurality of light diffusion        elements, each light diffusion element capable of changing a        propagation direction of an incident light beam and illuminating        a corresponding illuminated region among a plurality of        illuminated regions;    -   an irradiation device configured to irradiate the optical        element with the coherent light beam so as to allow the coherent        light beam to scan each light diffusion element;    -   spatial light modulators, each spatial light modulator disposed        to position which overlap each illuminated region; and    -   projection optical systems, each projection optical system        projecting modulation image obtained on each spatial light        modulator on corresponding screen,    -   wherein the propagation direction of the coherent light beam        incident to each position of the optical element is changed by        the corresponding light diffusion element so that the coherent        light beam is illuminated on the corresponding illuminated        region.

In the fifth or sixth projection device of the present invention, theirradiation device may include:

-   -   a light source configured to generate the coherent light beam;        and    -   a scan device configured to change the propagation direction of        the coherent light beam from the light source and allow the        coherent light beam to scan each light diffusion element.

In the fifth or sixth projection device of the present invention, thelight diffusion element may be a lens array.

According to the present invention, there is provided a projection-typevideo display device including:

-   -   any one of the first to sixth projection device; and    -   screens on which modulation images obtained on the spatial light        modulators are projected.

According to the present invention, it is possible to display aplurality of videos, to allow speckles to be inconspicuous, and tominiaturize an optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a specific example of a first basicembodiment as a diagram illustrating the first basic embodiment amongembodiments of the present invention.

FIG. 2 is a diagram illustrating the illumination device illustrated inFIG. 1.

FIG. 3 is a diagram illustrating an exposing method for manufacturing ahologram recording medium constituting an optical element of theillumination device illustrated in FIG. 2.

FIG. 4 is a diagram illustrating functions of the hologram recordingmedium manufactured by the exposing method illustrated in FIG. 3.

FIG. 5 is a perspective diagram illustrating functions of theillumination device illustrated in FIG. 1.

FIG. 6 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a specific example of a second basicembodiment as a diagram illustrating the second basic embodiment amongembodiments of the present invention.

FIG. 7 is a diagram illustrating an exposing method for manufacturing ahologram recording medium constituting an optical element of theillumination device illustrated in FIG. 6.

FIG. 8 is a diagram illustrating functions of the hologram recordingmedium manufactured by the exposing method illustrated in FIG. 7.

FIG. 9 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a first modified example of the second basicembodiment.

FIG. 10 is a schematic diagram illustrating configurations of anillumination device, a projection device, and a projection-type videodisplay device according to a second modified example of the secondbasic embodiment.

FIG. 11 is a perspective diagram illustrating a modified example of theirradiation device and functions thereof as a diagram corresponding toFIG. 5.

FIG. 12 is a perspective diagram illustrating another modified exampleof the irradiation device and functions thereof as a diagramcorresponding to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. Note that, in the drawings attached to thespecification, for the better understanding and the convenience ofillumination, reduction scales, aspect ratios, and the like areexaggerated differently from those of real objects.

A projection device and a projection-type video display device accordingto the embodiments of the present invention have a basic configurationcapable of effectively preventing speckles from occurring.

In the description hereinafter, first, a configuration which is capableof allowing speckles to be inconspicuous and displaying a plurality ofvideos and functions and effects which can be obtained based on theconfiguration will be described as a first basic embodiment withreference to a projection-type video display device including aprojection device illustrated in FIGS. 1 to 5. Next, a second basicembodiment having configurations different from those of the first basicembodiment will be described with reference to FIGS. 6 to 8. Next,modified embodiments of the configurations will be described.

First Basic Embodiment

Configuration of First Basic Embodiment

First, a configuration of a projection-type video display device whichincludes an illumination device and a projection device projectingcoherent light beams and which is capable of allowing speckles to beinconspicuous to display a plurality of videos will be described mainlywith reference to FIGS. 1 to 5.

The projection-type video display device 10 illustrated in FIG. 1includes three screens 15-1, 15-2, and 15-3 and a projection device 20which projects video images including coherent light beams. Theprojection device 20 includes an illumination device 40 whichsimultaneously illuminates three illuminated regions LZ1, LZ2, and LZ3located on a virtual plane with the coherent light beams, three spatiallight modulators 30-1, 30-2, and 30-3 which are disposed at positionsoverlapping the illuminated regions LZ1 to LZ3 and are illuminated withthe coherent light beams by the illumination device 40, and threeprojection optical systems 25-1, 25-2, and 25-3 which project eachmodulation image obtained on each of the spatial light modulators 30-1to 30-3 to the corresponding screen 15-1 to 15-3 respectively.

For example, a transmission-type liquid crystal micro display may beused as the spatial light modulators 30-1 to 30-3. In this case, each ofthe spatial light modulators 30-1 to 30-3 which are illuminated in aplanar shape by the illumination device 40 selectively transmits thecoherent light beam for each pixel, so that each of the modulationimages are formed on the screen of each display constituting each of thespatial light modulators 30-1 to 30-3. The modulation images (videoimages) obtained in this manner are changed in magnification andprojected to the corresponding screens 15-1 to 15-3 by the projectionoptical systems 25-1 to 25-3. Therefore, the modulation images aredisplayed on the screens 15-1 to 15-3 with changed magnification(generally, enlargement), so that an observer can observe the threeimages.

Note that, a reflection-type micro display may be used as the spatiallight modulators 30-1 to 30-3. In this case, the modulation images areformed by reflected light beams of the spatial light modulators 30-1 to30-3, and the plane irradiated with the coherent light beams illuminatedfrom the illumination device 40 to the spatial light modulators 30-1 to30-3 and the plane of the video images constituting the modulationimages progressing from the spatial light modulators 30-1 to 30-3 arethe same plane. In the case where the reflected light beams are used, aMEMS element such as a DMD (Digital Micromirror Device) may be used asthe spatial light modulators 30-1 to 30-3. In the apparatus disclosed inthe Patent Literature 2 described above, the DMD is used as a spatiallight modulator.

In addition, it is preferable that the incidence planes of the spatiallight modulators 30-1 to 30-3 have the same shape and size as those ofthe illuminated regions LZ1 to LZ3 which are illuminated with thecoherent light beams by the illumination device 40. This is because, inthis case, the coherent light beams of the illumination device 40 can beused to display videos on the screens 15-1 to 15-3 with high useefficiency.

The screens 15-1 to 15-3 may be configured as transmission-type screensor as reflection-type screens. In the case where the screens 15-1 to15-3 are configured as reflection-type screens, an observer observes avideo displayed by the coherent light beams reflected by the screens15-1 to 15-3 from the same side as the projection device 20 with respectto the screens 15-1 to 15-3. On the other hand, in the case where thescreens 15-1 to 15-3 are configured as transmission-type screens, theobserver observes a video displayed by the coherent light beams passingthrough the screens 15-1 to 15-3 from the side opposite to theprojection device 20 with respect to the screens 15-1 to 15-3.

The coherent light beams projected on the screens 15-1 to 15-3 arediffused to be recognized as videos by an observer. At this time, thecoherent light beams projected on the screens interfere with each otherdue to the diffusion, so that speckles occur. However, in theprojection-type video display device 10 described herein, theillumination device 40 described hereinafter is configured to illuminatethe illuminated regions LZ1 to LZ3, where the spatial light modulators30-1 to 30-3 are overlapped, with the coherent light beams of whichangles are changed in time. More specifically, although the illuminationdevice 40 described hereinafter illuminates the illuminated regions LZ1to LZ3 with diffused light beams including the coherent light beams, theincident angle of the diffused light beams is changed in time. As aresult, the diffusion pattern of the coherent light beams on the screens15-1 to 15-3 is also changed in time, and the speckles occurring due tothe diffusion of the coherent light beams overlap in time, so that thespeckles are inconspicuous. Hereinafter, the illumination device 40 willbe described more in detail.

The illumination device 40 illustrated in FIGS. 1 and 2 includes anoptical element 50 which divides a coherent light beam into three lightbeams and directs propagation directions of the divided light beamstoward the illuminated regions LZ1 to LZ3 and an irradiation device 60which irradiates the optical element 50 with the coherent light beam.The optical element 50 includes a hologram recording medium 55 which canreproduce the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3. Inthe example illustrated, the optical element 50 is composed of thehologram recording medium 55.

In the example illustrated, the hologram recording medium 55constituting the optical element 50 receives the coherent light beamilluminated from the irradiation device 60 as the reproductionillumination light beam La, diffracts the coherent light beam with highefficiency, and divides the coherent light beam. Particularly, thehologram recording medium 55 diffracts the coherent light beam which isincident to each position thereof, that is, a micro region which is tobe called each point thereof, and the coherent light beam is dividedinto three light beams, the image 5-1 of the scattering plate 6-1, theimage 5-2 of the scattering plate 6-2, and the image 5-3 of thescattering plate 6-3 can be simultaneously reproduced.

In other words, the hologram recording medium 55 allows the image of thescattering plate corresponding to each illuminated region to bereproduced in the illuminated regions LZ1 to LZ3. In addition, theimages 5-1 to 5-3 of the scattering plates 6-1 to 6-3 are multiplexedlyrecorded at each position of the hologram recording medium 55. In otherwords, in the hologram recording medium 55, information is multiplexedlyrecorded in each position so as to allow a coherent light beam to bediffused to a plurality of regions.

On the other hand, the irradiation device 60 irradiates the opticalelement 50 with the coherent light beam so as to allow the coherentlight beam of the hologram recording medium 55 to scan the hologramrecording medium 55 of the optical element 50. Therefore, in someinstant, a region of the hologram recording medium 55 which isirradiated with the coherent light beam by the irradiation device 60 isa portion of the surface of the hologram recording medium 55, andparticularly, in the example illustrated, the region is the micro regionwhich is to be called a point.

Next, the coherent light beam which is irradiated from the irradiationdevice 60 to scan the hologram recording medium 55 is incident to eachposition (each point or each region (the same will apply hereinafter))on the hologram recording medium 55 with an incident angle satisfying adiffraction condition of the hologram recording medium 55. Particularly,as illustrated in FIG. 2, the coherent light beam incident from theirradiation device 60 to each position of the hologram recording medium55 is allowed to reproduce the images 5-1 to 5-3 of the scatteringplates 6-1 to 6-3 corresponding to each illuminated region on theilluminated regions LZ1 to LZ3. In other words, the coherent light beamincident from the irradiation device 60 to each position of the hologramrecording medium 55 is diffused (spread) and divided by the opticalelement 50 to be incident on the illuminated regions LZ1 to LZ3. Inother words, in some instant, the coherent light beam incident tocertain position of the hologram recording medium 55 is illuminated onthe entire region of each of the illuminated regions LZ1 to LZ3. Inother words, the spatial light modulators 30-1 to 30-3 are illuminatedwith the coherent light beam which is incident from the irradiationdevice 60 to the hologram recording medium 55 to be diffused to aplurality of the illuminated regions LZ1 to LZ3.

In the example illustrated, a transmission-type volume hologram using aphotopolymer is used as the hologram recording medium 55 which enablesthe diffraction function of the coherent light beam. As illustrated inFIG. 3, the hologram recording medium 55 is manufactured by usingscattered light beams from the scattering plates 6-1 to 6-3 of a realobject as the object light beams Lo1, Lo2, and Lo3. FIG. 3 illustrates astate where the hologram photosensitive material 58 havingphotosensitivity which is to constitute the hologram recording medium 55is exposed by the reference light beams Lr1, Lr2 and Lr3 and the objectlight beams Lo1 to Lo3 which are the coherent light beams having mutualcoherence.

For example, laser beams from three laser sources which oscillate thelaser beams in a specific wavelength range are used as the referencelight beams Lr1 to Lr3, and the reference light beams Lr1 to Lr3 passthrough the light collection element 7 including lenses tosimultaneously be incident on the hologram photosensitive material 58.In the example illustrated in FIG. 3, the laser beams constituting thereference light beams Lr1 to Lr3 are incident on the light collectionelement 7 as the parallel light flux which is parallel to the opticalaxis of the light collection element 7. The reference light beams Lr1 toLr3 pass through the light collection element 7, so that the referencelight beams Lr1 to Lr3 are shaped (transformed) from the parallel lightflux to a converging light flux to be incident on the hologramphotosensitive material 58. At this time, the focal points FP ofconverging light fluxes Lr1 to Lr3 are located beyond the hologramphotosensitive material 58. In other words, the hologram photosensitivematerial 58 is disposed between the light collection element 7 and thefocal points FP of converging light fluxes Lr1 to Lr3 which arecollected by the light collection element 7.

Next, the object light beams Lo1 to Lo3 as scattered light beams fromthe scattering plates 6-1 to 6-3 made of, for example, an opal glass, onwhich the illumination light beams L1 to L3 are incident, are incidenton the hologram photosensitive material 58. Since the hologram recordingmedium 55 which is to be manufactured herein is a transmission-typehologram recording medium, the object light beams Lo1 to Lo3 areincident from the same plane as those of the reference light beams Lr1to Lr3 to the hologram photosensitive material 58. The object light beamLo1 needs to have coherence with the reference light beam Lr1.Similarly, the object light beam Lo2 needs to have coherence with thereference light beam Lr2, and the object light beam Lo3 needs to havecoherence with the reference light beam Lr3. On the other hand, it ispreferable that the object light beam Lo1 have no coherence with thereference light beams Lr2 and Lr3. Similarly, it is preferable that theobject light beam Lo2 have no coherence with the reference light beamsLr1 and Lr3, and the object light beam Lo3 have no coherence with thereference light beams Lr1 and Lr2. Therefore, for example, the laserbeam oscillated from the same first laser source may be divided into twolight beams, the one divided light beam may be used as the referencelight beam Lr1 described above, and the other may be used as theillumination light beam L1. Similarly, the reference light beam Lr2 andthe illumination light beam L2 may be generated by using the secondlaser source, and the reference light beam Lr3 and the illuminationlight beam L3 may be generated by using the third laser source. Thelaser beams from the first to third laser sources have the samewavelength.

In the example illustrated in FIG. 3, with respect to the scatteringplate 6-1, the parallel light flux of the illumination light beam L1parallel to the normal direction of the plate plane of the scatteringplate 6-1 is incident on the scattering plate 6-1 and scattered, and thescattered light beam passing through the scattering plate 6-1 isincident on the hologram photosensitive material 58 as the object lightbeam Lo1. According to this method, in the case where an isotropicscattering plate which is generally available at low cost is used as thescattering plate 6-1, the object light beam Lol from the scatteringplate 6-1 can be incident on the hologram photosensitive material 58with a substantially uniform light amount distribution. In addition,according to this method, although the light amount distribution dependson the degree of scattering of the scattering plate 6-1, the objectlight beam Lo1 is easily incident from the entire area of the lightemitting plane 6 a of the scattering plate 6-1 to each position of thehologram photosensitive material 58 with a substantially uniform lightamount. In this case, it can be realized that the light beam, which isincident to each position of the hologram recording medium 55 obtained,reproduces the image 5-1 of the scattering plate 6-1 with the samebrightness, and the reproduced image 5-1 of the scattering plate 6-1 isobserved with substantially uniform brightness. The same description canbe made with respect to the scattering plates 6-2 and 6-3.

In this manner, if the hologram recording material 58 is exposed by thereference light beams Lr1 to Lr3 and the object light beams Lo1 to Lo3,the interference fringe is generated by interference between thereference light beam Lr1 and the object light beam Lo1, the interferencefringe is generated by interference between the reference light beam Lr2and the object light beam Lot, and the interference fringe is generatedby interference between the reference light beam Lr3 and the objectlight beam Lo3. The interference fringes of these light beams aremultiplexedly recorded in the hologram recording material 58 as acertain pattern (in the volume hologram, as an example, a refractiveindex modulation pattern). After that, appropriate post processescorresponding to the type of the hologram recording material 58 areperformed, so that the hologram recording medium 55 is obtained.

In addition, the hologram recording medium 55 may be manufactured asfollows. In the manufacturing method, the reference light beam Lr1 andthe illumination light beam L1 which are generated by using one lasersource are used. First, interference fringe is generated on the hologramrecording material 58 by the reference light beam Lr1 and the objectlight beam Lo1 obtained from the illumination light beam L1 by usingonly the diffusion plate 6-1 of FIG. 3. Next, interference fringe isgenerated on the hologram recording material 58 by the reference lightbeam Lr1 and the object light beam Lot obtained from the illuminationlight beam L1 by using only the diffusion plate 6-2. Finally,interference fringe is generated on the hologram recording material 58by the reference light beam Lr1 and the object light beam Lo3 obtainedfrom the illumination light beam L1 by using only the diffusion plate6-3. After that, appropriate post processes corresponding to the type ofthe hologram recording material 58 are performed, so that the hologramrecording medium 55 is obtained. With respect to the diffusion plates6-1 to 6-3, the same diffusion plate may be used.

FIG. 4 illustrates a diffraction function (reproduction function) of thehologram recording medium 55 obtained through the exposing process ofFIG. 3. As illustrated in FIG. 4, with respect to the hologram recordingmedium 55 formed from the hologram photosensitive material 58 of FIG. 3,the light beam having the same wavelength as that of the laser beam usedfor the exposing process, which propagates in the reverse directionalong the optical path of the reference light beam Lr in the exposingprocess, satisfies the Bragg condition. In other words, as illustratedin FIG. 4, the diverging flux, which diverges from the standard point SPlocated with respect to the hologram recording medium 55 which has thesame positional relationship as the relative position (refer to FIG. 3)of the focal point FP with respect to the hologram photosensitivematerial 58 during the exposing process and has the same wavelength asthat of the reference light beam Lr during the exposing process, isdiffracted as the reproduction illumination light beam La by thehologram recording medium 55, so that the reproduced images 5-1 to 5-3of the scattering plates 6-1 to 6-3 are generated at a specificpositions with respect to the hologram recording medium 55 which havethe same positional relationship as the relative positions (refer toFIG. 3) of the scattering plates 6-1 to 6-3 with respect to the hologramphotosensitive material 58 during the exposing process.

The reproduced image 5-1 of the scattering plate 6-1 will be considered.At this time, the reproduction light beam (light beam obtained bydiffracting the reproduction illumination light beam La with thehologram recording medium 55) Lb1 which generates the reproduced image5-1 of the scattering plate 6-1 reproduces each point of the image 5-1of the scattering plate 6-1 as a light beam which propagates in thereverse direction along the optical path of the object light beam Lo1which propagates from the scattering plate 6-1 toward the hologramphotosensitive material 58 during the exposing process. Then, asdescribed above, as illustrated in FIG. 3, the object light beam Lo1 asthe scattered light beam which emits from each position of the lightemitting plane 6a of the scattering plate 6-1 during the exposingprocess is diffused (spread) so as to be incident on the substantiallyentire region of the hologram photosensitive material 58. In otherwords, the object light beam Lo1 from the entire region of the lightemitting plane 6a of the scattering plate 6-1 is incident to eachposition on the hologram photosensitive material 58, so that informationof the entire light emitting plane 6 a is recorded in each position ofthe hologram recording medium 55. Therefore, each light beamconstituting the diverging flux from the standard point SP whichfunction as the reproduction illumination light beam La illustrated inFIG. 4 is individually incident to each position of the hologramrecording medium 55, so that the images 5-1 of the scattering plate 6-1having the same contour can be reproduced at the same position(illuminated region LZ1). The same description can be made with respectto the images 5-2 and 5-3 of the scattering plates 6-2 and 6-3.

On the other hand, the irradiation device 60 which irradiates theoptical element 50 including the hologram recording medium 55 with thecoherent light beam may be configured as follows. In the exampleillustrated in FIGS. 1 and 2, the irradiation device 60 includes a lasersource 61 a which generates a coherent light beam and a scan device 65which changes the propagation direction of the coherent light beam fromthe laser source 61. The scan device 65 changes the propagationdirection of the coherent light beam in time, so that the propagationdirection of the coherent light beam is not a constant direction butvarious directions. As a result, the coherent light beam of which thepropagation direction is changed by the scan device 65 is allowed toscan the incidence plane of the hologram recording medium 55 of theoptical element 50.

Particularly, in the example illustrated in FIG. 2, the scan device 65includes the reflection device 66 having the reflection plane 66 a whichcan rotate about one axial line RA1. More specifically, the reflectiondevice 66 is configured as a mirror device having a mirror as thereflection plane 66 a which can rotate about one axial line RA1. Then,as illustrated in FIGS. 2 and 5, the mirror device 66 changes theorientation of the mirror 66 a to change the propagation direction ofthe coherent light beam from the laser source 61 a. At this time, asillustrated in FIG. 2, the mirror device 66 substantially receives thecoherent light beam from the laser source 61 a at the standard point SP.Therefore, the coherent light beam of which the propagation direction isfinally adjusted by the mirror device 66 can be incident on the hologramrecording medium 55 of the optical element 50 as the reproductionillumination light beam La (refer to FIG. 4) which can constitute onelight beam of the diverging flux from the standard point SP. As aresult, the coherent light beam from the irradiation device 60 isallowed to scan the hologram recording medium 55, and the coherent lightbeam incident to each position of the hologram recording medium 55 isallowed to reproduce the image 5-1 of the scattering plate 6-1 havingthe same contour at the same position (illuminated region LZ1), toreproduce the image 5-2 of the scattering plate 6-2 having the samecontour at the same position (illuminated region LZ2), and to reproducethe image 5-3 of the scattering plate 6-3 having the same contour at thesame position (illuminated region LZ3).

Note that, the mirror device 66 illustrated in FIG. 2 is configured torotate the mirror 66 a along one axial line RA1. FIG. 5 is a perspectivediagram illustrating a configuration of the illumination device 40illustrated in FIG. 2. In the example illustrated in FIG. 5, therotation axial line RA1 of the mirror 66 a is extended in parallel tothe Y axis of the XY coordinate system defined on the plate plane of thehologram recording medium 55 (that is, the XY coordinate system wherethe XY plane is parallel to the plate plane of the hologram recordingmedium 55). Then, since the mirror 66 a rotates about the axial line RA1which is parallel to the Y axis of the XY coordinate system defined onthe plate plane of the hologram recording medium 55, the incidence pointIP of the coherent light beam from the irradiation device 60 to theoptical element 50 is reciprocally moved in the direction which isparallel to the X axis of the XY coordinate system defined on the plateplane of the hologram recording medium 55. In other words, in theexample illustrated in FIG. 5, the irradiation device 60 irradiates theoptical element 50 with the coherent light beam so that the coherentlight beam is allowed to scan the hologram recording medium 55 along thestraight line path.

Note that, as a practical problem, there is a case where the hologramrecording material 58 is contracted during the manufacturing of thehologram recording medium 55. In this case, by taking into considerationthe shrinkage of the hologram recording material 58, it is preferablethat the recording angles of the coherent light beams, which isirradiated on the optical element 50 by the irradiation device 60, isadjusted. Therefore, the wavelength of the coherent light beam generatedby the coherent light source 61 a needs not to be strictly equal to thewavelength of the light beam used in the exposing process (recordingprocess) of FIG. 3, but the wavelengths thereof may be substantiallyequal to each other.

In addition, for the same reason, although the propagation directions ofthe light beams incident on the hologram recording medium 55 of theoptical element 50 are not taken to be strictly equal to the one lightbeam constituting the diverging flux from the standard point SP, theimages 5-1 to 5-3 can be reproduced in the illuminated regions LZ1 toLZ3. Actually, in the example illustrated in FIGS. 2 and 5, the mirror(reflection plane) 66 a of the mirror device 66 constituting the scandevice 65 is necessarily shifted from the rotation axial line RA1.Therefore, in the case where the mirror 66 a is allowed to rotate aboutthe rotation axial line RA1 which does not pass through the standardpoint SP, the light beam incident on the hologram recording medium 55may not be one light beam constituting the diverging flux from thestandard point SP. However, in a practical case, the coherent light beamfrom the irradiation device 60 having the illustrated configuration isallowed to substantially overlappedly reproduce the image 5-1 in theilluminated region LZ1. The same description can be made with respect tothe images 5-2 and 5-3.

Functions and Effects of First Basic Embodiment

Next, the functions of the illumination device 40, the projection device20, and the projection-type video display device 10 having theconfiguration described hereinbefore will be described.

First, the irradiation device 60 irradiates the optical element 50 withthe coherent light beam so as to allow the coherent light beam to scanthe hologram recording medium 55 of the optical element 50. Morespecifically, the laser source 61 a generates a coherent light beamhaving a specific wavelength which propagates in a constant direction,and the scan device 65 can change a propagation direction of thecoherent light beam. The scan device 65 allows the coherent light beamhaving a specific wavelength to be incident to each position of thehologram recording medium 55 with an incident angle satisfying the BraggCondition of the position. As a result, due to the diffraction anddivision on the hologram recording medium 55, the coherent light beamincident to each position overlappedly reproduces the image 5-1 of thescattering plate 6-1 in the illuminated region LZ1, overlappedlyreproduces the image 5-2 of the scattering plate 6-2 in the illuminatedregion LZ2, and overlappedly reproduces the image 5-3 of the scatteringplate 6-3 in the illuminated region LZ3. In other words, the coherentlight beam incident to a certain position is simultaneously illuminatedon the illuminated regions LZ1 to LZ3. In other words, the coherentlight beam incident from the irradiation device 60 to each position ofthe hologram recording medium 55 is diffused (spread) by the opticalelement 50 and divided so as to be incident on the entire region of eachof the illuminated regions LZ1 to LZ3. In this manner, the irradiationdevice 60 irradiates the illuminated regions LZ1 to LZ3 with thecoherent light beams.

As illustrated in FIG. 1, in the projection device 20, the spatial lightmodulators 30-1 to 30-3 are disposed at the positions which overlap theilluminated regions LZ1 to LZ3 of the illumination device 40. Therefore,with respect to the spatial light modulators 30-1 to 30-3, the planesthereof are illuminated by the illumination device 40, and each pixel isallowed to selectively transmit the coherent light beam, so that threevideos are formed. Each video is projected on the corresponding screens15-1 to 15-3 by the corresponding projection optical systems 25-1 to25-3. The coherent light beams projected on the screens 15-1 to 15-3 arediffused and recognized as videos by an observer. However, at this time,the coherent light beams projected on the screen interfere with eachother due to the diffusion, so that speckles occur.

However, according to the illumination device 40 of the first basicembodiment described herein, as described below, it is possible to veryeffectively allow the speckles to be inconspicuous. Since the specklescan be allowed to be inconspicuous according to the same principle withrespect to the illuminated regions LZ1 to LZ3, the descriptionhereinafter is made on only the illuminated region LZ1.

The Non Patent Literature 1 described above discloses that multiplexingof parameters of polarization, phase, angle, and time and increasing ofmodes are effective to allow the speckles to be inconspicuous. Herein,the modes denote speckle patterns having no correlation therebetween.For example, in the case where the coherent light beams from a pluralityof the laser sources are projected on the same screen in differentdirections, the number of the modes is equal to the number of the lasersources exist. In addition, in the case where the coherent light beamfrom the same laser source is projected on the screen in differentdirections in a time division manner, the number of the modes is equalto the number of changing of the incident direction of the coherentlight beam within a time which may not be resolved by human eyes. Then,it is considered that, in the case where a plurality of the modes exist,the interference patterns of light beams overlap each other with nocorrelation to be averaged, so that the speckles observed withobserver's eyes are inconspicuous.

In the irradiation device 60 described above, the coherent light beam isirradiated on the optical element 50 so as to scan the hologramrecording medium 55. In addition, with respect to the coherent lightbeams incident from the irradiation device 60 to the positions of thehologram recording medium 55, although the entire region of the sameilluminated region LZ1 is illuminated with the coherent light beam, theillumination directions of the coherent light beams which areilluminated on the illuminated region LZ1 are mutually different. Then,since the position on the hologram recording medium 55 where thecoherent light beam is incident is changed in time, the incidentdirection of the coherent light beam incident on the illuminated regionLZ1 is also changed in time.

If the illuminated region LZ1 is considered as a standard, although thecoherent light beam is consistently incident to the positions inside theilluminated region LZ1, the incident direction is always continuouslychanged as indicated by arrow A1 in FIG. 1. As a result, the light beamconstituting each pixel of the video formed by the transmitted lightbeam of the spatial light modulator 30-1 is projected on specificposition of the screen 15-1 while the optical path is changed in time asindicated by arrow A2 in FIG. 1.

Note that, the coherent light beam is allowed to continuously scan thehologram recording medium 55. Accordingly, the incident direction of thecoherent light beam incident from the irradiation device 60 to theilluminated region LZ1 is also continuously changed, and the incidentdirection of the coherent light beam incident from the projection device20 to the screen 15-1 is also continuously changed. Here, if theincident direction of the coherent light beam incident from theprojection device 20 to the screen 15-1 is changed by only a smallamount (for example, several deci-degrees), the pattern of specklesoccurring on the screen 15-1 is also greatly changed, so that specklepatterns having no correlation overlap. In addition, the frequency ofthe scan device 65 such as a MEMS mirror or a polygon mirror which isactually commercially available is typically several hundred Hz or more,and in some cases, the frequency of the scan device 65 may be severaltens of thousands of Hz.

Hereinbefore, according to the first basic embodiment described above,the incident direction of the coherent light beam is changed in time ateach position of each of the screens 15-1 to 15-3 displaying videos, andthe speed of the change thereof is such a speed that the change may notbe distinguished by human eyes, and thus, the multiplexed scatteringpatterns of the coherent light beams having no correlation are observedby human eyes. Therefore, the speckles occurring corresponding to thescattering patterns overlap to be averaged and are observed by anobserver. Therefore, with respect to the observer who observes thevideos displayed on the screens 15-1 to 15-3, the speckles are veryeffectively allowed to be inconspicuous.

Note that, with respect to the speckles observed by human in the relatedart, the speckles of the screen side may occur due to the scattering ofthe coherent light beams on the screens 15-1 to 15-3, and the specklesof the projection device side may occur due to the scattering of thecoherent light beams before projection on the screens. The specklepattern occurring at the projection device side is projected on thescreens 15-1 to 15-3 through the spatial light modulators 30-1 to 30-3,so that the speckle pattern can be recognized by the observer. However,according to the basic embodiment described above, the coherent lightbeam is allowed to continuously scan the hologram recording medium 55,and the coherent light beam which is incident to each position of thehologram recording medium 55 is illuminated on the entire regions of theilluminated regions LZ1 to LZ3 which the spatial light modulators 30-1to 30-3 overlap. In other words, the hologram recording medium 55 formsa new wavefront differently from the existing wavefront which forms thespeckle pattern, and illuminates complicatedly and uniformly theilluminated regions LZ1 to LZ3 and the screens 15-1 to 15-3 through thespatial light modulators 30-1 to 30-3. Due to the formation of the newwavefront by the hologram recording medium 55, the speckle patternoccurring at the projection device side may not be visually perceived.

The Non Patent Literature 1 described above discloses a method of usinga numerical value called speckle contrast as a parameter indicating adegree of speckles occurring on the screen. When a video of a testpattern which needs to have an originally uniform luminance distributionis displayed, the video on the screen actually have a variation inluminance. The speckle contrast is a quantity defined as a valueobtained by dividing a standard deviation of the variation in luminanceby an average value of luminance. As the value of the speckle contrastis increased, the degree of occurrence of speckles on the screen isincreased, and thus, a punctate luminance irregularity pattern is moreremarkably represented to an observer.

Hereinafter, the speckle contrast on the screen 15-1 will be described.In the projection-type video display device 10 according to the basicembodiment described with reference to FIGS. 1 to 5, the specklecontrast on the screen 15-1 is measured to be 3.0% (Condition 1). Inaddition, in the case where, instead of the reflection-type volumehologram, a relief type hologram which is a computer generated hologram(CGH) having a convex-concave shape designed by using a computer so asto generate an image 5-1 of the scattering plate 6-1 when a specificreproduction illumination light beam is received is used as the opticalelement 50 described above, the speckle contrast is measured to be 3.7%(Condition 2). In the application of HDTV (high definition TV) videodisplay, although a criterion that the speckle contrast is equal to orless than 6.0% is set (for example, refer to WO/2001/081996) as a levelthat an observer may not almost recognize the luminance irregularitypattern through visual observation, the basic embodiment described abovesatisfies the criterion. In addition, actually, in visual observation,luminance irregularity (brightness irregularity) to a degree that it canbe visually perceived does not occur.

On the other hand, in the case where the laser beam from the lasersource is shaped to be in the parallel light flux and is incident on thespatial light modulator 30-1, that is, in the case where the coherentlight beam from the laser source 61 a as the parallel light flux isincident on the spatial light modulator 30-1 of the projection-typevideo display device 10 illustrated in FIG. 1 without use of the scandevice 65 and the optical element 50, the speckle contrast becomes 20.7%(Condition 3). Under the condition, punctate luminance irregularitypatterns are very conspicuously observed through visual observation.

In addition, in the case where the light source 61 a is replaced with agreen LED (incoherent light source) and the light beam from the LEDlight source is incident on the spatial light modulator 30-1, that is,in the case where the incoherent light beam from the LED light source asthe parallel light flux is incident on the spatial light modulator 30-1of the projection-type video display device 10 illustrated in FIG. 1without use of the scan device 65 and the optical element 50, thespeckle contrast becomes 4.0% (Condition 4). Under the condition,luminance irregularity (brightness irregularity) to a degree that it canbe perceived through visual observation does not occur.

The results of Conditions 1 and 2 are much better than the result ofCondition 3, and the results of Conditions 1 and 2 are better than themeasurement result of Condition 4. As described above, the problem ofoccurrence of speckles is practically an intrinsic problem occurring inthe case of using a coherent light source such as a laser source, andthus, the problem needs not be considered in the case of an apparatususing an incoherent light source such as an LED. In addition, incomparison with Condition 4, in Conditions 1 and 2, the optical element50 which may cause occurrence of speckles is added. In terms of thispoint, it is considered that it is possible to sufficiently cope withthe speckle defect according to Conditions 1 and 2.

In addition, according to the first basic embodiment described above,the following advantages can be obtained.

According to the first basic embodiment described above, the opticalelement 50 for allowing the speckles to be inconspicuous may alsofunction as an optical member for dividing the coherent light beamirradiated from the irradiation device 60 into three light beams,changing the angles of the divided light beams, and shaping andadjusting the shapes of the divided light beams. Therefore, it ispossible to miniaturize and simplify the optical system. In addition,the transmission of the light becomes easy.

In addition, according to the first basic embodiment described above,since the videos corresponding to the screens can be simultaneouslydisplayed on the three screens 15-1 to 15-3, it is possible to increasean amount of display information in comparison with the projection-typevideo display device displaying video on only one screen. In addition,it is possible to perform panorama display where one video is displayedover the three screens 15-1 to 15-3 in a seamless manner. Therefore, theprojection-type video display device according to the basic embodimentcan be used as a display having a high sense of realization.

In addition, according to the first basic embodiment described above,the coherent light beam which is incident to each position of thehologram recording medium 55 allows the image 5-1 of the scatteringplate 6-1 to be generated at the mutually same first position, allow theimage 5-2 of the scattering plate 6-2 to be generated at the mutuallysame second position, and allow the image 5-3 of the scattering plate6-3 to be generated at the mutually same third position. Further, thespatial light modulators 30-1 to 30-3 are disposed to overlap the images5-1 to 5-3. Therefore, the light beam diffracted by the hologramrecording medium 55 can be used for video formation with highefficiency, so that use efficiency of the light from the light source 61a is excellent.

Second Basic Embodiment

A second basic embodiment relates to a projection device and aprojection-type video display device displaying a plurality of videos byusing a hologram recording medium different from that of the first basicembodiment. More specifically, the hologram recording medium accordingto the second basic embodiment includes three regions, and an image of adiffusion plate is recorded in each region.

Configuration of Second Basic Embodiment

First, the configuration of the projection-type video display devicewill be described with reference to FIG. 6, and the description is mademainly on different components from the first basic embodiment.

As illustrated in FIG. 6, the optical element 50 includes the hologramrecording medium 55 a which can reproduce the image of the scatteringplate corresponding to each illuminated region on the illuminatedregions LZ1 to LZ3. In addition, the hologram recording medium 55 aincludes three regions 55 a-1, 55 a-2, and 55 a-3 corresponding to theimages 5-1 to 5-3 of the scattering plates 6-1 to 6-3. In other words,on the hologram recording medium 55 a, in the region 55 a-1, the image5-1 of the corresponding scattering plate 6-1 is recorded, in the region55 a-2, the image 5-2 of the corresponding scattering plate 6-2 isrecorded, and in the region 55 a-3, the image 5-3 of the correspondingscattering plate 6-3 is recorded. In the example illustrated, theoptical element 50 is composed of the hologram recording medium 55 a.Other configurations are the same as those of the first basic embodimentof FIG. 1. Therefore, the same components are denoted by the samereference numerals, and the description thereof is not repeated.

In the example illustrated, the hologram recording medium 55 a receivesthe coherent light beam irradiated from the irradiation device 60 as thereproduction illumination light beam La to diffract the coherent lightbeam with high efficiency. Particularly, the hologram recording medium55 a diffracts the coherent light beam which is incident to eachposition existing in the region 55 a-1, that is, a micro region which isto be called each point existing in the region 55 a-1, so that the image5-1 of the scattering plate 6-1 can be reproduced in the illuminatedregion LZ1. Similarly, the hologram recording medium 55 a diffracts thecoherent light beam which is incident to each position of the region 55a-2, so that the image 5-2 of the scattering plate 6-2 can be reproducedin the illuminated region LZ2; and the hologram recording medium 55 adiffracts the coherent light beam which is incident to each position ofthe region 55 a-3, so that the image 5-3 of the scattering plate 6-3 canbe reproduced in the illuminated region LZ3.

On the other hand, the irradiation device 60 irradiates the opticalelement 50 with the coherent light beam so as to allow the coherentlight beam of the hologram recording medium 55 a to scan the hologramrecording medium 55 a of the optical element 50. Therefore, in someinstant, a region of the hologram recording medium 55 a which isirradiated with the coherent light beam by the irradiation device 60 isa portion of the surface of the hologram recording medium 55 a, andparticularly, in the example illustrated, the region is the micro regionwhich is to be called a point. In other words, in some instant, themicro region of any one of the regions 55 a-1 to 55 a-3 of the hologramrecording medium 55 a is irradiated with the coherent light beam.

Next, as illustrated in FIG. 6, the coherent light beam incident fromthe irradiation device 60 to each position existing in each of theregions 55 a-1 to 55 a-3 of the hologram recording medium 55 aoverlappedly reproduces the images 5-1 to 5-3 of the scattering plates6-1 to 6-3 corresponding to each of the regions 55 a-1 to 55 a-3 in thecorresponding illuminated regions LZ1 to LZ3. In other words, thecoherent light beam incident from the irradiation device 60 to eachposition of the region 55 a-1 of the hologram recording medium 55 a isdiffused (spread) by the optical element 50 so as to be incident on theilluminated region LZ1. Similarly, the coherent light beam incident toeach position of the region 55 a-2 of the hologram recording medium 55 ais diffused (spread) by the optical element 50 so as to be incident onthe illuminated region LZ2. In addition, the coherent light beamincident to each position of the region 55 a-3 of the hologram recordingmedium 55 a is diffused (spread) by the optical element 50 so as to beincident on the illuminated region LZ3. In other words, in some instant,the coherent light beam incident to a certain position of the hologramrecording medium 55 a is illuminated on the entire region of any one ofthe illuminated regions LZ1 to LZ3. In this manner, each of the spatiallight modulators 30-1 to 30-3 is illuminated with the coherent lightbeam which is incident from the irradiation device 60 to each of theregions 55 a-1 to 55 a-3 of the hologram recording medium 55 a to bediffused.

As illustrated in FIG. 7, the hologram recording medium 55 a ismanufactured by using the scattered light beams from the scatteringplates 6-1 to 6-3 of real objects as the object light beams Lo1, Lo2,and Lo3. FIG. 7 illustrates a state where the hologram photosensitivematerial 58 having photosensitivity which is to constitute the hologramrecording medium 55 a is exposed by the reference light beam Lr and theobject light beam Lo1 which are mutually coherent. Herein, an example ofthree divided steps of exposing the hologram photosensitive material 58will be described. In other words, as illustrated in FIG. 7, in a firststep, the regions 55 a-2 and 55 a-3 are covered with a mask 100 blockinglight, and only the region 55 a-1 is exposed by the reference light beamLr and the object light beam Lo1 obtained from the scattering plate 6-1.In a second step, the regions 55 a-1 and 55 a-3 are covered with themask 100 blocking light, and only the region 55 a-2 is exposed by thereference light beam Lr and the object light beam Lo2 obtained from thescattering plate 6-2 (not illustrated). In a third step, the regions 55a-1 and 55 a-2 are covered with the mask 100 blocking light, and onlythe region 55 a-3 is exposed by the reference light beam Lr and theobject light beam Lo3 obtained from the scattering plate 6-3 (notillustrated).

For example, a laser beam from the laser source which oscillates a laserbeam in a specific wavelength range is used as the reference light beamLr, and the reference light beam Lr passes through the light collectionelement 7 including lenses to be incident on the hologram photosensitivematerial 58.

In the first step, the object light beam Lo1 as a scattered light beamfrom the scattering plate 6-1 made of, for example, an opal glass, onwhich the illumination light beam L is incident, is incident on thehologram photosensitive material 58. The object light beam Lo1 needs tohave coherence with the reference light beam Lr. Therefore, for example,a laser beam oscillated from the same laser source may be divided, oneof the divided beams may be used as the reference light beam Lrdescribed above, and the other may be used as the illumination lightbeam L.

In this manner, if the hologram recording material 58 is exposed by thereference light beam Lr and the object light beam Lo1, the interferencefringe is generated by interference between the reference light beam Lrand the object light beam Lo1, and the interference fringe of the lightbeams is recorded in the hologram recording material 58 as a certainpattern (for example, in the case of a volume hologram, a refractiveindex modulated pattern). After that, similarly, the above-describedsecond and third steps of exposure are performed. At the last,appropriate post processes corresponding to the type of the hologramrecording material 58 are performed, so that the hologram recordingmedium 55 a is obtained.

FIG. 8 illustrates a diffraction function (reproduction function) of thehologram recording medium 55 a obtained through the exposing process ofFIG. 7. As illustrated in FIG. 8, with respect to the hologram recordingmedium 55 a formed from the hologram photosensitive material 58 of FIG.7, the light beam having the same wavelength as that of the laser beamused for the exposing process, which propagates in the reverse directionalong the optical path of the reference light beam Lr in the exposingprocess, satisfies the Bragg condition. In other words, as illustratedin FIG. 8, the diverging flux, which diverges from the standard point SPlocated with respect to the hologram recording medium 55 a which has thesame positional relationship as the relative position (refer to FIG. 7)of the focal point FP with respect to the hologram photosensitivematerial 58 during the exposing process and has the same wavelength asthat of the reference light beam Lr during the exposing process, isdiffracted as the reproduction illumination light beam La by thehologram recording medium 55 a, so that the reproduced images 5-1 to 5-3of the scattering plates 6-1 to 6-3 are generated at a specificpositions with respect to the hologram recording medium 55 which havethe same positional relationship as the relative positions (refer toFIG. 7) of the scattering plates 6-1 to 6-3 with respect to the hologramphotosensitive material 58 during the exposing process.

The region 55 a-1 of the hologram recording medium 55 a will beconsidered. At this time, the reproduction light beam (light beamobtained by diffracting the reproduction illumination light beam La withthe hologram recording medium 55) Lb1 which generates the reproducedimage 5-1 of the scattering plate 6-1 reproduces each point of the image5-1 of the scattering plate 6-1 as a light beam which propagates in thereverse direction along the optical path of the object light beam Lolwhich propagates from the scattering plate 6-1 toward the hologramphotosensitive material 58 during the exposing process. Then, asdescribed above, as illustrated in FIG. 7, the object light beam Lo1 asthe scattered light beam which emits from each position of the lightemitting plane 6 a of the scattering plate 6-1 during the exposingprocess is diffused (spread) so as to be incident on the substantiallyentire region of the region 55 a-1 of the hologram photosensitivematerial 58. In other words, the object light beam Lo1 from the entireregion of the light emitting plane 6 a of the scattering plate 6-1 isincident to each position of the region 55 a-1 on the hologramphotosensitive material 58, so that information of the entire lightemitting plane 6a is recorded in each position of the region 55 a-1 ofthe hologram recording medium 55 a. Therefore, each light beamconstituting the diverging flux from the standard point SP whichfunction as the reproduction illumination light beam La illustrated inFIG. 8 is individually incident to each position of the region 55 a-1 ofthe hologram recording medium 55 a, so that the images 5-1 of thescattering plate 6-1 having the same contour can be reproduced at thesame position (illuminated region LZ1). The same description can be madewith respect to the regions 55 a-2 and 55 a-3.

Functions and Effects of Second Basic Embodiment

Next, the functions of the illumination device 40, the projection device20, and the projection-type video display device 10 having theconfiguration described hereinbefore will be described.

First, the irradiation device 60 irradiates the optical element 50 withthe coherent light beam so as to allow the coherent light beam to scanthe hologram recording medium 55 a of the optical element 50. Morespecifically, the laser source 61 a generates a coherent light beamhaving a specific wavelength which propagates in a constant direction,and the scan device 65 can change a propagation direction of thecoherent light beam. The scan device 65 allows the coherent light beamhaving a specific wavelength to be incident to each position of thehologram recording medium 55 a with an incident angle satisfying theBragg Condition of the position. As a result, the coherent light beamincident to each position existing in each of the regions 50 a-1 to 50a-3 overlappedly reproduces the images 5-1 to 5-3 of the scatteringplates 6-1 to 6-3 corresponding to each of the regions 55 a-1 to 55 a-3in the corresponding illuminated regions LZ1 to LZ3. More specifically,due to the diffraction on the hologram recording medium 55 a, thecoherent light beam incident to each position existing in the region 50a-1 overlappedly reproduces the image 5-1 of the scattering plate 6-1 inthe illuminated region LZ1. Similarly, the coherent light beam incidentto each position existing in the region 50 a-2 overlappedly reproducesthe image 5-2 of the scattering plate 6-2 in the illuminated region LZ2,and the coherent light beam incident to each position existing in theregion 50 a-3 overlappedly reproduces the image 5-3 of the scatteringplate 6-3 in the illuminated region LZ3. In other words, the coherentlight beam incident from the irradiation device 60 to each positionwhich exists in each of the regions 50 a-1 to 50 a-3 of the hologramrecording medium 55 a is diffused (spread) by the optical element 50 soas to be incident on the entire region of the corresponding illuminatedregions LZ1 to LZ3. In this manner, the irradiation device 60 irradiatesthe illuminated regions LZ1 to LZ3 with the coherent light beams.

As described above, in some instant, the coherent light beam incident toa certain position existing in the region 50 a-1 of the hologramrecording medium 55 a is illuminated on the entire region of theilluminated region LZ1. Therefore, at this time, the illuminated regionsLZ2 and LZ3 are not illuminated. In other words, the coherent light beamis allowed to scan the hologram recording medium 55 a, so that any oneof the illuminated regions LZ1 to LZ3 is illuminated one by one. If thescan speed of the coherent light beam scanning the hologram recordingmedium 55 a is appropriately set, the existence of the time period whenthe illuminated regions LZ1 to LZ3 are not illuminated cannot berecognized by an observer.

As described in the first basic embodiment, in the projection device 20illustrated in FIG. 6, the spatial light modulators 30-1 to 30-3 aredisposed at the positions which overlap the illuminated regions LZ1 toLZ3 of the illumination device 40. Therefore, with respect to thespatial light modulators 30-1 to 30-3, the planes thereof areilluminated by the illumination device 40, and each pixel is allowed toselectively transmit the coherent light beam, so that three videos areformed. Each video is projected on the corresponding screens 15-1 to15-3 by the corresponding projection optical systems 25-1 to 25-3. Thecoherent light beams projected on the screens 15-1 to 15-3 are diffusedand recognized as videos by an observer. However, at this time, thecoherent light beams projected on the screen interfere with each otherdue to the diffusion, so that speckles occur.

However, according to the illumination device 40 of the second basicembodiment described herein, it is possible to very effectively allowthe speckles to be inconspicuous by the same principle as that of thefirst basic embodiment.

In other words, according to the second basic embodiment describedabove, the incident direction of the coherent light beam is changed intime at each position of each of the screens 15-1 to 15-3 displayingvideos, and the speed of the change thereof is such a speed that thechange may not be distinguished by human eyes, and thus, the multiplexedscattering patterns of the coherent light beams having no correlationare observed by human eyes. Therefore, the speckles occurringcorresponding to the scattering patterns overlap to be averaged and areobserved by an observer. Therefore, with respect to the observer whoobserves the videos displayed on the screens 15-1 to 15-3, the specklesare very effectively allowed to be inconspicuous.

In addition, according to the second basic embodiment described above,similarly to the first basic embodiment, the following advantages can beobtained.

According to the second basic embodiment described above, opticalelement 50 for allowing the speckles to be inconspicuous may alsofunction as an optical member for dividing the coherent light beamirradiated from the irradiation device 60 into three light beams,changing the angles of the divided light beams, and shaping andadjusting the shapes of the divided light beams. Therefore, it ispossible to miniaturize and simplify the optical system.

In addition, according to the second basic embodiment described above,since the videos corresponding to the screens can be simultaneouslydisplayed on the three screens 15-1 to 15-3, it is possible to increasean amount of display information in comparison with the projection-typevideo display device displaying video on only one screen. In addition,it is possible to perform panorama display where one video is displayedover the three screens 15-1 to 15-3 in a seamless manner. Therefore, theprojection-type video display device according to the basic embodimentcan be used as a display having a high sense of realization.

In addition, according to the second basic embodiment described above,the coherent light beam which is incident to each position of the region55 a-1 of the hologram recording medium 55 a allows the image 5-1 of thescattering plate 6-1 to be generated at the mutually same firstposition. Similarly, the coherent light beam which is incident to eachposition of the region 55 a-2 allows the image 5-2 of the scatteringplate 6-2 to be generated at the mutually same second position, and thecoherent light beam which is incident to each position of the region 55a-3 allows the image 5-3 of the scattering plate 6-3 to be generated atthe mutually same third position. Further, the spatial light modulators30-1 to 30-3 are disposed so as to overlap the images 5-1 to 5-3.Therefore, the light beam diffracted by the hologram recording medium 55a can be used for video formation with high efficiency, so that useefficiency of the light from the light source 61 a is excellent.

Note that, instead of the hologram recording medium 55 a having theregions 55 a-1 to 55 a-3, three hologram recording media correspondingto the regions 55 a-1 to 55 a-3 may be combined.

Modifications of First and Second Basic Embodiments

The first and second embodiments described above based on one specificexample exemplified in FIGS. 1 to 8 can be modified in various forms.Hereinafter, modified examples will be described with reference to thedrawings. In the drawings used for the description hereinafter, thecomponents corresponding to those of the embodiments described above aredenoted by the same reference numerals, and the description thereof willnot be repeated.

Projection Device

In the basic embodiment, the example where each of the spatial lightmodulators 30-1 to 30-3 is disposed at the position which overlaps thecorresponding illuminated regions LZ-1 to LZ-3 is described. However,each of the spatial light modulators 30-1 to 30-3 may not be disposed atthe position which strictly overlaps the corresponding illuminatedregions LZ-1 to LZ-3. For example, in the configuration of the firstbasic embodiment of FIG. 1, the spatial light modulator 30-1 may bedisposed to the optical element 50 side rather than the illuminatedregion LZ-1, and the spatial light modulator 30-1 may be disposed to theprojection optical system 25-1 side rather than the illuminated regionLZ-1. The same description can be made with respect to the spatial lightmodulators 30-2 and 30-3. In other words, in the first basic embodiment,the hologram recording medium 55 and the spatial light modulators 30-1to 30-3 may be disposed so that the coherent light beam, which isincident to each position of the hologram recording medium 55 to bediffused, overlappedly illuminates on a plurality of the spatial lightmodulators 30-1 to 30-3. In addition, in the second basic embodiment,the hologram recording medium 55 a and the spatial light modulators 30-1to 30-3 may be disposed so that the coherent light beam, which isincident to each position existing in each of the regions 55 a-1 to 55a-3 of the hologram recording medium 55 a to be diffused, overlappedlyilluminates on the corresponding spatial light modulators 30-1 to 30-3.

First Modified Example of Second Basic Embodiment

In the second basic embodiment, the coherent light beam is allowed toscan the hologram recording medium 55 a, so that any one of theilluminated regions LZ1 to LZ3 is illuminated one by one. On thecontrary, as illustrated in FIG. 9, the three laser sources (lightsource units) 61 a-1 to 61 a-3 may be configured to be used to allow thecoherent light beams to simultaneously scan the regions 55 a-1 to 55 a-3of the hologram recording medium 55 a, so that all the illuminatedregions LZ1 to LZ3 can be simultaneously illuminated.

In the example illustrated in FIG. 9, the mirror device 66 receives thecoherent light beams from the laser sources 61 a-1 to 61 a-3 roughly atthe standard point SP. Therefore, the coherent light beams of which thepropagation directions are finally adjusted by the mirror device 66 canbe incident on the hologram recording medium 55 a as the reproductionillumination light beams La1 to La3, each of which can constitute onelight beam of the diverging flux from the standard point SP. As aresult, the region 55 a-1 of the hologram recording medium 55 a receivesthe coherent light beam irradiated from the laser source 61 a-1 as thereproduction illumination light beam La1. Similarly, the region 55 a-2of the hologram recording medium 55 a receives the coherent light beamirradiated from the laser source 61 a-2 as the reproduction illuminationlight beam La2, and the region 55 a-3 receives the coherent light beamirradiated from the laser source 61 a-3 as the reproduction illuminationlight beam La3.

Therefore, the coherent light beams from the irradiation device 60 canbe allowed to simultaneously scan the regions 55 a-1 to 55 a-3 of thehologram recording medium 55 a. In addition, the coherent light beamincident to each position of the region 55 a-1 of the hologram recordingmedium 55 a is allowed to reproduce the image 5-1 of the scatteringplate 6-1 having the same contour at the same position (illuminatedregion LZ1), the coherent light beam incident to each position of theregion 55 a-2 is allowed to reproduce the image 5-2 of the scatteringplate 6-2 at the same position (illuminated region LZ2), and thecoherent light beam incident to each position of the region 55 a-3 isallowed to reproduce the image 5-3 of the scattering plate 6-3 at thesame position (illuminated region LZ3).

According to this modified example, since all the illuminated regionsLZ1 to LZ3 are simultaneously illuminated, the illumination device 40can illuminate the illuminated regions LZ1 to LZ3 more brightly.Therefore, brighter videos can be formed on the screens 15-1 to 15-3.

In addition, the same effects as those of the second basic embodimentcan be obtained.

Second Modified Example of Second Basic Embodiment

As illustrated in FIG. 10, the three laser sources 61 a-1 to 61 a-3 maybe disposed to be parallel to each other so that the reproductionillumination light beams La1 to La3 are allowed to be incident on thehologram recording medium 55 a as diverging light beams. In other words,in this configuration, the coherent light beams emitted from the lasersources 61 a-1 to 61 a-3 are incident to three positions of the scandevice 65 as parallel light beams, and the coherent light beam isreflected from each position toward the hologram recording medium 55 aas diverging light beam.

In this configuration, the region 55 a-1 of the hologram recordingmedium 55 a also receives the coherent light beam irradiated from thelaser source 61 a-1 as the reproduction illumination light beam La1.Similarly, the region 55 a-2 of the hologram recording medium 55 areceives the coherent light beam irradiated from the laser source 61 a-2as the reproduction illumination light beam La2, and the region 55 a-3receives the coherent light beam irradiated from the laser source 61 a-3as the reproduction illumination light beam La3.

According to this modified example, the coherent light beams irradiatedon the mirror plane of the scan device 65 are dispersed, and thus,strong light beam is not irradiated on specific position of the mirrorplane, so that durability of the scan device 65 is improved.

In addition, it is possible to obtain the same effects as those of thesecond basic embodiment and the first modified example of the secondbasic embodiment.

Note that, a laser array configured by integrating three laser sourcesmay be used as the laser sources 61 a-1 to 61 a-3.

A portion of the coherent light beam from the irradiation device 60passes through the hologram recording medium 55 a without diffraction bythe hologram recording medium 55 a. The light beam is called azeroth-order light beam. If the zeroth-order light beam is incident onthe illuminated regions LZ1 to LZ3, abnormal regions (punctate region,linear region, planar region) where brightness (luminance) is sharplyincreased in comparison with peripheral regions occur in the illuminatedregions LZ1 to LZ3.

In case of using the reflection-type hologram recording medium (notillustrated), since the spatial light modulators 30-1 to 30-3 and theprojection optical systems 25-1 to 25-3 are not disposed in thedirection where the zeroth-order light beam propagates, the zeroth-orderlight beam can be relatively easily avoided. However, in the case ofusing the transmission-type hologram recording medium 55 a illustratedin FIG. 9 or the like, since the spatial light modulator 30 and theprojection optical system 25 are highly likely to be disposed in thedirection close to the direction where the zeroth-order light beampropagates, careful treatment is necessary.

In the case of using the transmission-type hologram recording medium 55a, for example, in the configuration illustrated in FIG. 10, althoughthe zeroth-order light beam passes through the hologram recordingmedium, since the spatial light modulators 30-1 to 30-3 and theprojection optical systems 25-1 to 25-3 are not disposed in thedirection, the zeroth-order light beam is highly likely to be avoided.However, in the configuration illustrated in FIG. 9, since the opticalpath of the coherent light beam reflected by the light scan unit 50 maybe changed, the zeroth-order light beam may pass through the spatiallight modulators 30-1 to 30-3 or the projection optical system 25.Therefore, even in the case of employing the configuration illustratedin FIG. 9, the light scan unit 50, the spatial light modulators 30-1 to30-3, and the projection optical systems 25-1 to 25-3 are designed to bedisposed according to the propagating path of the zeroth-order lightbeam so that the zeroth-order light beam cannot pass through the spatiallight modulators 30-1 to 30-3 or the projection optical systems 25-1 to25-3.

Spatial Light Modulator, Projection Optical System, and Screen

According to the first and second embodiments described above, it ispossible to effectively allow speckles to be inconspicuous. However, thefunctions and effects are obtained mainly from the illumination device40. Then, in the case where the illumination device 40 is configured asa combination of various existing spatial light modulators, projectionoptical systems, screens, and the like, the speckles are effectivelyallowed to be inconspicuous. Due to this point, the spatial lightmodulators, the projection optical systems, and the screens are notlimited to the exemplified ones, but various existing members, parts,apparatuses, and the like may be used.

Projection-Type Video Display Device

In addition, although the example where the hologram recording medium 55(55 a) is manufactured by using the planar scattering plates 6-1 to 6-3having a shape corresponding to the incidence planes of the spatiallight modulators 30-1 to 30-3 and by an interference exposing method isillustrated, the present invention is not limited thereto. The hologramrecording medium 55 (55 a) may be manufactured by using a scatteringplate having some pattern and by an interference exposing method. Inthis case, the image of the scattering plate having some pattern isreproduced by the hologram recording medium 55 (55 a). In other words,the optical element 50 (hologram recording medium 55 (55 a)) illuminatesthe illuminated regions LZ1 to LZ3 having some patterns. In the casewhere the optical element 50 is used, the spatial light modulators 30-1to 30-3 and the projection optical systems 25-1 to 25-3 may be omittedfrom the first and second basic embodiments described above, and thescreens 15-1 to 15-3 are disposed at the positions which overlap theilluminated regions LZ1 to LZ3, so that some patterns recorded in thehologram recording medium 55 (55 a) can be displayed on the screens 15-1to 15-3. In this display device, the irradiation device 60 irradiatesthe optical element 50 with the coherent light beams so that thecoherent light beams are allowed to scan the hologram recording medium55 (55 a), so that it is possible to allow the speckles to beinconspicuous on the screens 15-1 to 15-3.

Irradiation Device

In the first and second embodiments described above, an example wherethe irradiation device 60 includes the laser source 61 a and the scandevice 65 is illustrated. Although the scan device 65 which isconfigured with one-axis-rotation type mirror device 66 which changesthe propagation direction of the coherent light beam by reflection isexemplified, the scan device 65 is not limited thereto. As illustratedin FIG. 11, the scan device 65 may be configured so that themirror(reflection plane 66 a) of the mirror device 66 can rotate aboutthe first rotation axial line RA1 as well as about the second rotationaxial line RA2 intersecting the first rotation axial line RA1. FIG. 11illustrates an example where the modified example is applied to thefirst basic embodiment. In the example illustrated in FIG. 11, thesecond rotation axial line RA2 of the mirror 66 a is perpendicular tothe first rotation axial line RA1 which is extended in parallel to the Yaxis of the XY coordinate system defined on the plate plane of thehologram recording medium 55. Then, since the mirror 66 a can rotateabout both of the first axial line RA1 and the second axial line RA2,the incidence point IP of the coherent light beam from the irradiationdevice 60 incident on the optical element 50 can be moved on the plateplane of the hologram recording medium 55 in two-dimensional directions.Therefore, as an example, as illustrated in FIG. 11, the incidence pointIP of the coherent light beam incident on the optical element 50 mayalso be configured to be moved along a circumference. At this time,similarly to the first basic embodiment, the coherent light beamincident to each incidence point IP can be simultaneously illuminated onthe illuminated regions LZ1 to LZ3. Note that, in FIG. 11, for betterunderstanding, the reproduction light beams to the illuminated regionsLZ1 and LZ3 are not illustrated.

In the case where the modified example is applied to the second basicembodiment, the scan path may be configured so that the incidence pointIP is moved in the regions 55 a-1 to 55 a-3 of the hologram recordingmedium 55 a.

In addition, the scan device 65 may include two or more mirror devices66. In this case, although the mirror 66 a of the mirror device 66 canrotate about only one axial line, the incidence point IP of the coherentlight beam from the irradiation device 60 incident on the opticalelement 50 can be moved on the plate plane of the hologram recordingmedia 55 and 55 a in the two-dimensional directions.

Note that, as a specific example of the mirror devices 66 a included inthe scan device 65, there are a MEMS mirror, a polygon mirror, and thelike.

In addition, the scan device 65 may be configured to include a devicebesides a reflection device (for example, the mirror device 66 describedabove) which changes the propagation direction of the coherent lightbeam through reflection. For example, the scan device 65 may include arefraction prism or lens or the like.

Essentially, the scan device 65 is not a necessary component. The lightsource 61 a of the irradiation device 60 is configured so that the lightsource can be displaced (moved, oscillated, and rotated) with respect tothe optical element 50 and so that the coherent light beams irradiatedfrom the light source 61 a are allowed to scan the hologram recordingmedium 55 (55 a) according to the displacement of the light source 61 awith respect to the optical element.

Further, although the description hereinbefore is made under thepresumption that the light source 61 a of the irradiation device 60oscillates a laser beam which is shaped as a linear light beam, thepreset invention is not limited thereto. Particularly, in the firstbasic embodiment described above, the coherent light beam irradiated oneach position of the optical element 50 is shaped as the light fluxeswhich are to be incident on the illuminated regions LZ1 to LZ3 by theoptical element 50. In addition, in the second basic embodimentdescribed above, the coherent light beam irradiated on each positionexisting in each region of the optical element 50 is shaped as the lightflux which is to be incident on the entire region of the illuminatedregions LZ1 to LZ3 corresponding to each region by the optical element50. Therefore, even in the case where the coherent light beam irradiatedfrom the light source 61a of the irradiation device 60 on the opticalelement 50 is not accurately shaped, no problem occurs. For this reason,the coherent light beam generated from the light source 61 a may be adiverging light beam. In addition, the shape of cross section of thecoherent light beam generated from the light source 61 a may be anellipse or the like instead of a circle. In addition, the transversemode of the coherent light beam generated from the light source 61 a maybe a multi-mode.

Note that, in the case where the light source 61 a generates thediverging flux, when the coherent light beam is incident on the hologramrecording medium 55 (55 a) of the optical element 50, the light beam isincident on not a spot but a region having somewhat area. In this case,the light beam which is diffracted by the hologram recording medium 55(55 a) to be incident to each position of the illuminated regions LZ1 toLZ3 is multiplexed in terms of angle. In other words, in each instant,the coherent light beams are incident from the directions of certainangle ranges to each position of the illuminated regions LZ1 to LZ3. Dueto the multiplexing in terms of angle, it is possible to moreeffectively allow the speckles to be inconspicuous.

Further, in the first and second embodiments described above, althoughthe example where the irradiation device 60 allows the coherent lightbeam to be incident on the optical element 50 so as to trace the opticalpath of the one light beam constituting the diverging flux is described,the present invention is not limited thereto. For example, in the firstand second embodiments described above, as illustrated in FIG. 12, thescan device 65 may be configured to further include a collection lens(parallel light generation unit) 67 disposed at the lower stream side ofthe mirror device 66 along the optical path of the coherent light beam.FIG. 12 illustrates an example where the modified example is applied tothe first basic embodiment. In this case, the light beam from the mirrordevice 66, which propagates along the optical path of the light beamconstituting the diverging flux, is allowed by the collection lens 67 tobecome the light beam which propagates in a certain direction. In otherwords, the irradiation device 60 allows the coherent light beam to beincident on the optical element 50 so as to trace the optical path ofthe light beam constituting the parallel light flux. In this example, inthe exposing process during the manufacturing of the hologram recordingmedium 55, instead of the converging light flux described above, theparallel light flux is used as the reference light beam Lr. The hologramrecording medium 55 can be more simply manufactured and replicated.

The modified example may be applied to the second basic embodiment.

In the first and second embodiments described above, the example thatthe irradiation device 60 includes only one laser source 61 a isdescribed. However, the present invention is not limited thereto. Asalready described as the first and second modified examples of thesecond basic embodiment, in the first basic embodiment, for example, theirradiation device 60 may include a plurality of the light sources whichoscillate light beams having the same wavelength range. In this case,the illumination device 40 can illuminate the illuminated regions LZ1 toLZ3 more brightly. In addition, the coherent light beams from differentsolid-state laser sources have no mutual coherency. Therefore, themultiplexing of the scattering patterns further progresses, so that itis possible to allow the speckles to be more inconspicuous.

In addition, the irradiation device 60 may include a plurality of thelight sources which generate the coherent light beams having differentwavelength ranges. According to this example, a color which is hard todisplay by using a single laser beam is generated through additive colormixing, and the illuminated regions LZ1 to LZ3 can be illuminated withthe generated color. In addition, in this case, in the projection device20 or the transmission-type video display device 10, in the case wherethe spatial light modulators 30-1 to 30-3 include, for example, colorfilters and are capable of forming modulation image with respect to eachcoherent light beam having each wavelength range, the video can bedisplayed in a plurality of colors. Alternatively, although the spatiallight modulators 30-1 to 30-3 do not include color filters, in the casewhere the irradiation device 60 irradiates the coherent light beamhaving each wavelength range in a time division manner and the spatiallight modulators 30-1 to 30-3 operate in a time division manner so as toform modulation image corresponding to the irradiated coherent lightbeam having the wavelength range, the video can be displayed in aplurality of colors. Particularly, in the projection device 20 or thetransmission-type video display device 10, in the case where theirradiation device 60 includes a light source which generates thecoherent light beam having a wavelength range corresponding to redlight, a light source which generates the coherent light beam having awavelength range corresponding to green light, and a light source whichgenerates the coherent light beam having a wavelength rangecorresponding to blue light, the video can be displayed in full colors.

Note that, the hologram recording medium 55 (55 a) included in theoptical element 50 has wavelength selectivity. Therefore, in the casewhere the irradiation device 60 includes light sources having differentwavelength ranges, the hologram recording medium 55 (55 a) may beconfigured to include hologram components corresponding to thewavelength ranges of the coherent light beams generated from the lightsources in a laminated state. The hologram components for the coherentlight beams having the wavelength ranges may be manufactured by usingthe coherent light beams having the corresponding wavelength ranges asthe light beams for exposing (reference light beams Lr1 to Lr3 andobject light beams Lo1 to Lo3 or reference light beam Lr and objectlight beams Lo1 to Lo3), for example, in the method described above withreference to FIGS. 3, 4, 7, and 8. In addition, instead of manufacturingthe hologram recording medium 55 (55 a) by laminating the hologramcomponents for the wavelength ranges, the hologram photosensitivematerial 58 is simultaneously exposed with the object light beam andreference light beam which are obtained from the coherent light beamshaving the wavelength ranges, and a plurality of light beams havingwavelength ranges are diffracted by a single hologram recording medium55 (55 a).

Optical Element

In the embodiment described above, although the example where theoptical element 50 is configured with the reflection-type volumehologram recording medium 55 (55 a) using photopolymer is described, thepresent invention is not limited thereto. As described above, theoptical element 50 may include a plurality of the hologram recordingmedia 55 (55 a). In addition, the optical element 50 may include a typeof a volume hologram recording medium where recording is performed byusing a photosensitive medium including a silver halide material.Further, the optical element 50 may include a reflection-type volumehologram recording medium, and the optical element 50 may include arelief type (emboss type) hologram recording medium.

With respect to the relief type (emboss type) hologram recording medium,hologram interference fringe is recorded by using a convex-concavestructure of a surface thereof. However, in the case of the relief typehologram recording medium, since scattering due to the convex-concavestructure of the surface may also cause occurrence of new speckles, thevolume hologram recording medium is preferred. In the case of the volumehologram recording medium, hologram interference fringe is recorded byusing a refractive index modulation pattern (refractive indexdistribution) of an inner portion of the medium, there is no influenceof the scattering due to the convex-concave structure of the surface.

However, even in the case of the volume hologram recording medium, ifrecording is performed by using a photosensitive medium including asilver halide material, scattering due to silver halide particles mayalso cause occurrence of speckles. Therefore, as the hologram recordingmedium 55 (55 a), the volume hologram recording medium using aphotopolymer is preferred.

The reflection-type hologram recording medium is higher than thetransmission-type hologram recording medium in terms of the wavelengthselectivity. In other words, in the reflection-type hologram recordingmedium, although interference fringes corresponding to a differentwavelength are laminated, a coherent light beam having a desiredwavelength can be diffracted by using only a desired layer. In addition,in terms of removing the influence of the zeroth-order light beam, thereflection-type hologram recording medium is excellent.

On the other hand, although the transmission-type hologram recordingmedium has a wide diffractable spectrum range and a high degree ofallowance of the laser source, if interference fringes corresponding todifferent wavelengths are laminated, layers other than a desired layeralso diffract the coherent light beam having a desired wavelength.Therefore, in general, it is difficult to configure thetransmission-type hologram recording medium in a lamination structure.

In addition, in the exposing process illustrated in FIGS. 3 and 7,although a so-called Fresnel type hologram recording medium ismanufactured, a Fourier transform type hologram recording medium whichcan be obtained through recording using lenses may be manufactured.However, in the case of using a Fourier transform type hologramrecording medium, the lenses can be used even during the reproduction.

In addition, a striped pattern (refractive index modulation pattern orconvex-concave pattern) which is to be formed on the hologram recordingmedium 55 (55 a) may be designed by using a computer based onwavelengths or incident directions of predetermined reproductionillumination light beam La, shapes or positions of to-be-reproducedimages, and the like without use of the actual object light beam Lo andthe reference light beam Lr. The hologram recording medium 55 (55 a)obtained in this manner is called computer generated hologram recordingmedium. In addition, similarly to the modified example described above,in the case where a plurality of the coherent light beams havingmutually different wavelength ranges are irradiated from the irradiationdevice 60, the hologram recording medium 55 (55 a) as the computergenerated hologram recording medium may be configured so as to bepartitioned two-dimensionally into a plurality of regions disposedcorresponding to the coherent light beams having the wavelength ranges,and the coherent light beams having the wavelength ranges are diffractedby the corresponding regions to reproduce images.

Further, in the second basic embodiment described above, although theexample where the optical element 50 includes the hologram recordingmedium 55 a which spreads the coherent light beam irradiated to eachposition existing in each of the regions 55 a-1 to 55 a-3 andilluminates the entire region of the corresponding illuminated regionsLZ1 to LZ3 with the spread coherent light beam is described, the presentinvention is not limited thereto. Instead of the hologram recordingmedium 55 a or in addition to the hologram recording medium 55 a, theoptical element 50 may include a plurality of lens arrays (lightdiffusion elements) as optical components capable of changing thepropagation direction of the incident light beam and diffusing the lightbeam and illuminating the corresponding illuminated region among aplurality of the illuminated regions LZ1 to LZ3. As a specific exampleof the lens array, a total reflection-type or refraction-type Fresnellens added with a diffusion function, a fly-eye lens, or the like may beexemplified. In the illumination device 40, the irradiation device 60and the optical element 50 may also be configured so that theirradiation device 60 allows the coherent light beam to scan each lensarray, irradiates the optical element 50 with the coherent light beamand so that the propagation direction of the coherent light beamincident from the irradiation device 60 to each position of the opticalelement 50 is changed by the corresponding lens array to be illuminatedon the corresponding illuminated regions LZ1 to LZ3. Therefore, it ispossible to effectively allow the speckles to be inconspicuous.

Illuminating Method

In the first and second basic embodiments described above, as anexample, the irradiation device 60 is configured so as to allow thecoherent light beam to scan the optical element 50 in one-dimensionaldirection, and the hologram recording medium 55 (55 a) (or lens arrays)of the optical element 50 are configured so as to diffuse (spread,diverge) the coherent light beam irradiated to each position intwo-dimensional directions, so that the illumination device 40illuminates the illuminated regions LZ1 to LZ3 in a two-dimensionalmanner. However, as already explained, the present invention is notlimited thereto. For example, the irradiation device 60 may beconfigured so as to allow the coherent light beam to scan the opticalelement 50 in two-dimensional directions, and the hologram recordingmedium 55 (55 a) (or lens arrays) of the optical element 50 may beconfigured so as to diffuse (spread, diverge) the coherent light beamirradiated to each position in two-dimensional directions, so that theillumination device 40 illuminates the illuminated regions LZ1 to LZ3 ina two-dimensional manner (described above with reference to FIG. 11).

Combination of Modified Examples

Note that, although several modified examples of the first and secondbasic embodiments are described hereinbefore, it is obvious that acombination of a plurality of the modified examples is available.

Number of Screens

In the description hereinbefore, although the example where theprojection-type video display device 10 includes the three screens 15-1to 15-3 is described, the projection-type video display device 10 mayinclude two screens or four or more screens. In this case, in the firstbasic embodiment, the projection device may include the hologramrecording medium where images of the scattering plates, of which thenumber is equal to the number of screens, are multiplexedly recorded andthe spatial light modulators and the projection optical system, of whichthe respective number is equal to the number of screen. In addition, inthe second basic embodiment, the projection device may include thehologram recording medium which is partitioned into regions, of whichthe number is equal to the number of screens, and the spatial lightmodulator and the projection optical system, of which the respectivenumber is equal to the number of screens. In addition, the image of thescattering plate may be recorded in each region of the hologramrecording medium.

The invention claimed is:
 1. An illumination device comprising: anoptical element comprising a hologram recording medium capable ofdiffusing a coherent light beam, the hologram recording mediumcomprising a plurality of hologram recording medium regions, eachhologram recording medium region diffusing a coherent light beam to anilluminated region corresponding to the hologram recording mediumregion; and an irradiation device including a light source configured togenerate the coherent light beam and a scan device configured todistribute the coherent light beam from the light source to theplurality of hologram recording medium regions included in the hologramrecording medium, the irradiation device being configured to irradiatethe plurality of hologram recording medium regions with the coherentlight beam distributed from the light source to the plurality ofhologram recording medium regions so as to allow the coherent light beamto scan the plurality of hologram recording medium regions, wherein eachhologram recording medium region comprises a plurality of positions insuch hologram recording medium region, and for each hologram recordingmedium region, each coherent light beam incident to a position in suchhologram recording medium region is diffused to an entirety of therespective illuminated region corresponding to the hologram recordingmedium region in order to illuminate the entirety of the illuminatedregion.
 2. The illumination device according to claim 1, wherein anilluminated region corresponding to a hologram recording medium regionis shifted from an illuminated region corresponding to another hologramrecording medium region.
 3. The illumination device according to claim1, wherein the scan device is configured to change a propagationdirection of the coherent light beam from the light source and allow thecoherent light beam to scan the hologram recording medium.
 4. Theillumination device according to claim 3, wherein the coherent lightbeam from the light source is irradiated to one point of the scandevice, the coherent light beam reflected from the one point of the scandevice constitutes a diverging flux from the one point, and thediverging flux is incident on the hologram recording medium.
 5. Theillumination device according to claim 3, wherein the coherent lightbeam from the light source is irradiated to one point of the scandevice, and the coherent light beam reflected from the one point of thescan device constitutes a diverging flux from the one point, and whereinthe illumination device further comprises a parallel light generationunit which propagates each light beam constituting the diverging flux ina certain direction to generate parallel light flux and allows theparallel light flux to be incident on the hologram recording medium. 6.The illumination device according to claim 1, wherein the scan device isconfigured to change a propagation direction of the coherent light beamfrom the light source and allow the coherent light beam to scan thehologram recording medium, wherein the light source comprises aplurality of light source units which emit a plurality of coherent lightbeams, wherein a plurality of the coherent light beams emitted from aplurality of the light source units are illuminated to the same point onthe scan device, and wherein each coherent light beam reflected from thesame point on the scan device constitutes diverging flux from the samepoint, and each diverging flux is incident on the corresponding hologramrecording medium region.
 7. The illumination device according to claim1, wherein the scan device is configured to change a propagationdirection of the coherent light beam from the light source and allow thecoherent light beam to scan the hologram recording medium, wherein thelight source comprises a plurality of light source units which emit aplurality of coherent light beams in substantially parallel directions,wherein each coherent light beam emitted from a plurality of the lightsource units is irradiated at corresponding point on the scan device,and wherein each coherent light beam reflected at each point on the scandevice constitutes diverging flux from the corresponding each point, andeach diverging flux is incident on the corresponding hologram recordingmedium region.
 8. An illumination device comprising: an optical elementcomprising a plurality of light diffusion elements, each light diffusionelement capable of changing a propagation direction of an incident lightbeam, each light diffusion element diffusing a coherent light beam to anilluminated region corresponding to the light diffusion element; and anirradiation device including a light source configured to generate thecoherent light beam and a scan device configured to distribute thecoherent light beam from the light source to the plurality of lightdiffusion elements included in the optical element, the irradiationdevice being configured to irradiate the plurality of light diffusionelements with the coherent light beam distributed from the light sourceto the plurality of light diffusion elements so as to allow the coherentlight beam to scan the plurality of light diffusion elements, whereineach light diffusion element comprises a plurality of positions in saidlight diffusion element, and for each light diffusion element, eachcoherent light beam incident to a position in such light diffusionelement is diffused to an entirety of the respective illuminated regioncorresponding to the light diffusion element in order to illuminate theentirety of the illuminated region.
 9. The illumination device accordingto claim 8, wherein an illuminated region corresponding to a lightdiffusion element is shifted from an illuminated region corresponding toanother light diffusion element.
 10. The illumination device accordingto claim 8, wherein the scan device is configured to change thepropagation direction of the coherent light beam from the light sourceand allow the coherent light beam to scan each light diffusion element.11. The illumination device according to claim 8, wherein the opticalelement comprises a lens array.